The present invention relates to a method and a system of charging a propulsion battery of an electrically powered vehicle by inductively coupling a primary charger connected to a source of power with a secondary charger installed on a vehicle and connected to its battery.
Prior art publications such as U.S. Pat. Nos. 4,347,472, 4,496,896 and Publication of Unexamined Japanese Patent Application No. 63-73837 (1988) disclose apparatuses for charging a battery of an electrically powered vehicles, in which a charging unit having a secondary winding and mounted at the front end or the bottom of a vehicle is properly into an inductively coupled state with respect to a stationary battery charger provided at a charging station. In the inductively coupled state of the primary and secondary chargers, electrical energy applied across a winding in the primary charger is transferred to a winding in the secondary charger by electromagnetic induction.
U.S. Pat. No. 4,374,354 discloses a rechargeable electric portable appliance such as an electric toothbrush. In this appliance, the toothbrush unit, which carries at its bottom a secondary coil assembly with an E-shaped core as seen in cross section, is guided vertically and inserted within a well in a base unit containing a primary coil assembly with a similar E-shaped core, where magnetic coupling is established between the primary and secondary windings.
Still another prior art of Publication of Unexamined Japanese Patent Application No. 3-239137 (1991) proposes an inductive coupler which includes a secondary coil assembly having a guide along which the secondary coil assembly is moved into abutment of its core with a counterpart core of a primary coil assembly for ensuring proper mating between the paired cores to form a closed magnetic circuit.
In view of practical application in the future of battery-powered vehicles of various types from small vehicles, such as scooters and carts, to passenger cars and trucks of various sizes, it is desirable that each vehicle should be equipped with a battery whose output voltage suits the size or power requirement of that vehicle. To cope with the requirement of charging various batteries with the above charging apparatuses, it is necessary to change the induced secondary voltage to a desired level for each battery, which may be accomplished by changing the primary voltage to be applied across the winding in the primary battery charger. However, this method requires not only additional equipment for changing the primary voltage, but also troublesome operation of that equipment each time the type of battery to be charged is changed. Furthermore, power loss caused by the voltage changing cannot be overlooked.